L38 0. R. Wieland — Williamsonian Tribe. 



fronds, and fruits of "Williamsonian affinity, recovered from 

 the Khiit of Skone. First restored as a Williamsonia (li), 

 this interesting plant as it since transpires from renewed study 

 by the collodion method (21), has a staminate form Quite as 

 much reduced as, or even comparable to that of Tumboa, 

 necessitating the new genus ]Yi,laniHdla. 



More recently still, the validity of these determinations of 

 leaf and stem unity based mainly on data of association, has been 

 strongly confirmed by the writer's discovery of the recurrence 

 in the Rhjit-Liassic of the so-called " Mixteca Alta" of Oaxaca 

 in southern Mexico, of precisely the same association of stems, 

 leaves and Williamsonia buds as in the Gondwanas (22, 27). In 

 fact the general features of the Indian specimens are so nearly 

 repeated that Feistmantel's figures would well nigh answer for 

 their Oaxacan counterparts as shown in fig. 4 C. Similarity 

 even extends to the stem nodes of vertically compressed scars, 

 a most interesting feature completely establishing relationship 

 with Wielancliella, in which such nodes are also present and 

 must be due, since we know both the ovulate and staminate 

 fructification, to scars left by old leafy crowns or to bract 

 whorls enveloping the terminal branch and fruit buds follow- 

 ing stages of vegetative growth.* 



* The argument for the Williamsonian nature of these stems rests on their 

 notably close and persistent association with Williamsonia foliage in India 

 and Mexico, and the presence of the nodes of closer set horizontally 

 elongated scars as in Wielancliella. These nodes were noted by both Oldham 

 and Morris and Feistmantel (86), both of whom give figures clearly showing 

 the characters of these stems. Oldham and Morris in particular seem never 

 to have doubted their cycadaceous [and therefore Williamsonian !] nature, 

 since always found with Ptilophyllum and Dictyozamites (Dictyopteris) 

 foliage. But Feistmantel, though likewise supposing such stems to be 

 cycadaceous and Williamsonian, has m one instance (ref. 8, plate xiii, figs. 

 6 and 7) figured slender forms as Brachyphyllum, from which there is a real 

 difficulty of separation, it not being wholly certain that the nodes seen to 

 be characteristic of forms like those shown in figure 4 (n, n) are either 

 present in most Williamsoniae, or absent in all Brachyphylloideae. 



Indeed because of certain Cordaites-like characters common to both these 

 groups such difficulty of separation may even be expected to increase with 

 the rinding of new and more varied forms. Though setting anatomic char- 

 acters aside it would tax belief to now regard the node-bearing group of 

 stems as mainly Brachyphylloid instead of Williamsonian, in which case 

 leaves and fruits only of the latter type would uniformly accompany stems 

 only of the former in such widely separated localities as the Yorkshire coast, 

 India, and Mexico. Such anomalies of conservation and association may be 

 possible, but appear improbable. 



Regarding the nodes of laterally broadened and smaller scars alternant with 

 the long internodes of large vertically elongate and keeled rhombic scars 

 several explanations may be offered. But it appears from Nathorst's study 

 of Wielancliella (14) and the Paris Museum stem with leaves attached 

 figured by Wieland (20), that the long internodal spaces were occupied by 

 scale-leaves, the old bases of which thus really form quite three-fourths of 

 the thin armor. The general habitus is near to that of Cycas, which fully 

 explains why such stems have been hitherto regarded as Cycadacean. 



